Integrated optical package for coupling optical fibers to devices with asymmetric light beams

ABSTRACT

This invention embodies an integrated optical package including an optical component having an asymmetric modal output, and a lens integrated with the component for coupling to another optical component having a large modal area. The coupling is achieved by the use of a Polymeric Elongated Waveguide Emulating (PEWE) lens. In the exemplary embodiment the first optical component is a modulator, and the other optical component is an optical fiber. A facet of the modulator is etched by reactive ion etching (RIE) which allows integration of the PEWE lens on a common substrate. The lens is manufactured using a polymer film on a dielectric cladding layer. The fabrication relies on the remelt and reflow properties of polymer films to provide a smooth adiabatic mode contraction from a circular (optical fiber) mode (≈6 μm in diameter) to a semiconductor mode (≈1 μm) over a length of 250 μm. The PEWE lens permits coupling with an insertion loss of 0.5 dB and 80 percent coupling efficiency, even though the lens is butt-coupled to a fiber without any external lens. The PEWE lens allows the realization of better than 80 percent direct fiber butt-coupling efficiencies to semiconductor lasers, photodetectors, optical modulators, switches and amplifiers with a simultaneous order of magnitude relaxation of the alignment tolerances typically needed for the coupling of semiconductor devices with single-mode fibers.

TECHNICAL FIELD

The present invention relates to an integrated optical package includingan optical device with an asymmetric light mode, such as anelliptically-shaped light beam, and a lens for coupling the opticaldevice to an optical fiber.

BACKGROUND OF THE INVENTION

Future network systems may include long-haul optical communicationsystems, interconnection technologies, two dimensional opticalprocessing, optical computing and others. Semiconductor devices, such aslasers and photodetectors, are already an integral part of optical fibercommunication systems. In conjunction with fibers, other semiconductordevices, such as modulators and optical switches, are also likely to beincorporated into the network systems.

Unfortunately, the utility of many such semiconductor devices ishampered by their high fiber insertion loss which at least partiallyarises from a fundamental mismatch between a typical single-mode fiberwith a relatively large cylindrical core and, thus, a large circularmodal input or (output) area, and semiconductor devices having smallermodal output (or input) areas and eccentricity ratios greater than 1:1.Losses which arise in coupling light between optical fibers and thesedevices include those arising from the mismatch of the symmetry of thetwo modes (circular versus elliptical) as well as the mismatch of theaverage modal area.

In the past, symmetric hemispherically and hyperbolically shapedmicrolenses have been fabricated on the end of an optical fiber by meansof a pulsed laser beam. See U.S. Pat. No. 4,932,989, issued to H. M.Presby on Jun. 12, 1990 and U.S. Pat. No. 5,011,254 issued to C. A.Edwards and H. M. Presby on Apr. 30, 1991. Such microlenses affordrelatively high coupling efficiency for devices, such as lasers, havinga symmetric modal output, that is, for devices whose output beamprofiles are circular or have ellipticity ratios close to 1:1 i.e.,where the divergence of the output beam of the laser is the same orsubstantially the same along axes parallel and perpendicular to thejunction plane of the laser. Use of hyperbolically shaped microlensedfibers has led to greater than 90 percent coupling efficiencies betweenoptical fibers and devices having symmetric modal output. However, themodal asymmetry exhibited by many semiconductor devices requires, forgood coupling efficiencies, asymmetric microlenses. There are manylasers which have an elliptical beam structure with ellipticities fromabout 1:1.5 and even higher, emanating from the laser facet. Use ofsymmetric microlenses for coupling elliptical light beams to fibers, ledto significant decrease in the coupling efficiencies. For example, forsuch semiconductor devices as laser diodes with reasonable modalasymmetry, e.g. 1:2.5 to 1:3.5, fiber coupling efficiencies of up to 50percent can be obtained with symmetric microlenses, with 25 to 35percent being more typical. Since about half of the laser output is notutilized, the laser has to be run at higher currents to yield the samecoupled power into fiber than a more efficient coupling scheme couldgive. Running the laser at higher currents results in greater heat to bedissipated. For example, when the coupling efficiency is at 50 percent,the laser thermal power dissipation is four times greater than at 100percent coupling efficiency. This affects long-term stability andreliability of the lasers and presents a major obstacle in thedevelopment of uncooled laser diode technology. For modulators andswitches, where from a system design viewpoint an insertion loss of lessthan 0.5-1.0 dB is desired, the situation could be more serious. Ahigher, e.g. 3 dB, insertion loss decreases signal to noise ratio andincreases system complexity.

Attempts to increase coupling of fibers to elliptical beams withnon-symmetric lenses have been reported in the form of an externallymounted cylindrical lens and a wedge-shaped fiber endface. See M.Saruwatari et al. "Semiconductor Laser to Single-Mode Fiber Coupler,"Applied Optics, Vol. 18, No. 11, 1979, pages 1847-1856 and V. S. Shah etal. "Efficient Power Coupling from a 980 nm, Broad Area Laser to aSingle-Mode Fiber Using a Wedge-Shaped Fiber Endface", J. LightwaveTechnology, Vol. 8, No. 9, 1990, pages 1313-1318. In the former case thecoupling is effected by means of a lens and a cylindrical rod placedbetween a laser and an optical fiber, and in the latter case an end ofthe fiber is provided with an enlarged cylindrical portion terminatingin a wedge-like shape which approximates a cylindrical lens. In thelatter case, a coupling efficiency of 47 percent was obtained. Clearly,what is required for optimum coupling between a device with anelliptical light beam output (or input) area and an optical fiber is alens which would transform the elliptical beam output of the device tomatch the circular single-mode fiber mode profile and vice versa.

SUMMARY OF THE INVENTION

This invention embodies an integrated optical package including anoptical component having an asymmetric modal output, and a lensintegrated with the component for coupling to another optical componenthaving a large modal area. The coupling is achieved by the use of aPolymeric Elongated Waveguide Emulating (PEWE) lens. In the exemplaryembodiment the first optical component is a modulator and the otheroptical component is an optical fiber. A facet of the modulator isetched by reactive ion etching (RIE) which allows integration of thePEWE lens on a common substrate. The lens is manufactured using apolymer film on a dielectric cladding layer. The fabrication relies onthe remelt and reflow properties of polymer films to provide a smoothadiabatic mode contraction from a circular (optical fiber) mode (≈6 μmin diameter) to a semiconductor mode (≈1 μm) over a length of 250 μm.The PEWE lens permits coupling with an insertion loss of 0.5 dB and 80percent coupling efficiency, even though the lens is butt-coupled to afiber without any external lens. The PEWE lens allows the realization ofbetter than 80 percent direct fiber butt-coupling efficiencies tosemiconductor lasers, photodetectors, optical modulators, switches andamplifiers with a simultaneous order of magnitude relaxation of thealignment tolerances typically needed for the coupling of semiconductordevices. Single-mode fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an integrated optical package showing amicrolens coupling an optical device to an optical fiber;

FIG. 2 is a perspective view of the microlens;

FIG. 3 is an enlarged schematic representation of a side view of aportion of a compound semiconductor structure with a thin SiO₂ layerthereon prior to formation of the microlens;

FIG. 4 is a top view of the structure of FIG. 3 with a diamond-likeshaped photoresist region;

FIG. 5 is a schematic representation of a side view in cross-section ofthe structure of FIG. 4 with a continuous layer of photoresist over thewhole of the upper area;

FIG. 6 is a schematic representation of the structure after the heatingand reflow of the photoresists shown in FIG. 5;

FIG. 7 is a schematic representation of an angle light exposure of anarea of the photoresist to remove unwanted photoresist from an endportion of the microlens adjoining the device;

FIG. 8 shows the microlens after removal of the unwanted photoresistregion and prior to separation of two adjoining lenses along the centerline 27;

FIG. 9 is a schematic representation of an intermediate step in theformation of a polyimide microlens utilizing a reflown photoresist layeron top of the polymer layer;

FIG. 10 is a schematic representation of the polyimide microlens formedfrom the configuration of FIG. 9.

DETAILED DESCRIPTION

This invention embodies an integrated optical package including asemiconductor device having an elliptical mode output integrated with anelongated optical lens for coupling the device to an optical fiber witha circular mode and vice versa. The package and process steps used inthe fabrication of the package are described hereinbelow with referenceto the drawings. For illustration purposes, various dimensions of thedrawings are not drawn to scale.

Shown in FIG. 1 is a schematic perspective view representation of anintegrated optical coupling package, 10. Package 10 includes a compoundsemiconductor device, 11, having an asymmetric modal output area, and acoupling optical lens, 12, formed integrally with the device andcoupling an optical mode output (or input) of the device to an opticalfiber 13. Lens 12 is of an organic polymeric material includingphotoresists and other polymers. For smooth coupling of optical energyfrom the device to a fiber and vice versa, lens 12 is in the form of anelongated wedge-like waveguide. This lens may be referred to as aPolymeric Elongated Waveguide Emulating (PEWE) optical lens.

Typical semiconductor device 11 includes a semiconductor substrate, 14,a bottom cladding layer, 15, an active layer, 16, a top cladding layer17, and a lower and a top electrodes, 18 and 19, respectively. Thedevice may further include at least one other layer, such as a bufferlayer positioned between the substrate and the bottom cladding layer, ahighly doped contact layer positioned between the top cladding layer andthe top electrode, a capping layer positioned on top of the top claddingor contact layer, and some other layers depending on the construction ofthe device, as is well-known in the art. Undoped or lightly dopedtransition layers may also be deposited between the active layer and thecladding layers. The active layer may be a single layer, an alternatingmultilayer structure, or a structure graded on both sides of the activelayer. Such layers are well-known in the art and may vary depending onthe device.

A layer, 20, of an optically transparent dielectric material overlays atop surface, 21, of the device, its light-emitting (or light-receiving)facet, 22, and a surface, 23, of the bottom cladding layer 15. Prior todeposition of the dielectric layer, the surface of facet 22 may becoated with a light-reflective coating. Such coatings as AgBr or ZnS,are suitable for this purpose. Top surface 24 of layer 20 is alignedwith lower boundary of active layer 16. Lens 12 rests on top surface 24of layer 20 and abuts that portion of layer 20 which is in contact withfacet 22 of the device. Since the lower surface of lens 12 is on surface24 of layer 20, the bottom of the lens is also aligned with the bottomof active layer 16. To fit the lens to the cross-section of activeregion 16 and of the optical fiber, the lens is in the form of atruncated wedge. The narrower end of the wedge is aligned with andapproximates the cross-sectional area of active region 16, while thewider end of the wedge approximates the cross-section of at least thecore of the optical fiber. The face of the lens at the narrow end has arectangular-to-elliptical cross-section with an asymmetry ratio closelyapproximating that of the active region. The narrow end of the lensabuts facet 22 of device 11. The opposite face of the lens at the wideend has a square-to-circular or -elliptical cross-section whichapproximates at least the cross-section of the core of the opticalfiber. A perspective view of lens 12 without the dielectric layer andthe substrate is shown in FIG. 2. Optical fiber 13 is shown abutting thelens; however, it may be any other optical component with a relativelylarge modal area, relative to the modal area of the optical device 11.

A number of packages may be produced upon a single compoundsemiconductor wafer, and then divided out, e.g. by cleaving into singleor duplex packages or alternatively, into a parallel multiple of singleor duplex packages. A duplex integrated package includes twosemiconductor devices 11 integrally produced on the substrate in aback-to-back fashion permitting insertion of an optical radiation fromone optical fiber into one device via a related lens, transfer of theradiation from one device to another device, and then coupling of theradiation from said other device into another optical fiber via therelated lens.

The production of the integrated optical package begins with asemiconductor structure of the device upon a semiconductor wafer, formedby depositing on the substrate a plurality of different layers by planartechnology. The structure typically includes an active layer placedbetween a bottom and a top cladding layers but may include other layersas is well-known in the art.

At least one flat trench is etched in the surface of the semiconductorstructure exposing vertical facets 22. The width of each trench betweenthe facets is equal to twice the desired length of the lens. Thedistance between the trenches is selected to accommodate the length oftwo devices. Prior to forming the lenses, the etched facet may be coatedwith a thin antireflective coating, such as AgBr or ZnS. Thereafter, thebottom of each trench, the facet and the upper surface of each device,are coated with a thin layer of an optically transparent dielectricmaterial. The trench is of such depth and the dielectric material is ofsuch thickness that, when the dielectric material is deposited on thebottom of the trench, the upper surface of the dielectric material inthe trench is in alignment with the bottom boundary of the active layerin the structure. This assures alignment of the lower surface of thelens resting on the dielectric layer with the bottom boundary of theactive layer.

The lens is produced by depositing, on upper surface 24 of dielectriclayer 20 in the trench, a layer of an organic polymeric material,selected from photoresists and other polymers, which is opticallytransmissive and has an index of refraction approximating that of thecore of the optical fiber. The organic polymeric material afterprocessing has in a longitudinal cross-section a truncated wedge-likestructure the upper surface of which slopes from the wide, opticalfiber-mating end to the narrow, device-mating end. The thickness of theorganic material is small relative to the length of the lens so that theupper surface of the lens slopes gradually from the wide end to thenarrow end. In the preferred embodiment, the upper surface of the lensslopes from about 6-7 μm at the wide, optical fiber end to about 1 μm atthe device end over a length of about 250 μm. Thereafter, the organicpolymeric material is trimmed laterally, e.g., by plasma etching, toremove any organic polymeric material which is not needed for thetransmission of the radiation energy from the device to the fiber andvice versa. The top view of the lens has the shape of a truncatedtriangle, with the broader base facing the fiber and with the narrowerbase facing the device. Because of the gentle slope of the wedge, thereis little possibility of leakage of the radiation through theunprotected surfaces of the lens. To reduce even this possibility,exposed surfaces of the lens may be coated with a thin layer ofdielectric material, such as SiO₂ with n=1.47, which could block theleakage. Preferably, the coating material shall have an index ofrefraction which is lower than the material of the lens.

For illustration purposes, this invention is described with reference toan optical modulator waveguide, having an elliptical light mode with aratio of, e.g. 1:3, as the semiconductor device 11. This device iscoupled to an optical fiber by PEWE lens 12 fabricated from aphotoresist material having refractive index (n=1.63) approximating thatof the core (n=1.49-1.52) of the optical fiber. An effective fibercoupling efficiency of 80 percent with an order of magnitude relaxationof the typical alignment tolerances is obtainable with this arrangement.

Shown in FIG. 3 is an enlarged schematic representation of a section ofa compound semiconductor wafer acting as a semiconductor substrate witha GaAs/AlGaAs device structure grown thereon by planar technology. Inthe exemplary embodiment device 11 is a modulator having a structureincluding a 150 μm thick GaAs substrate 14, a 1.5 μm thick Al₀.4 Ga₀.6As bottom cladding layer 15, a 50 period GaAs/AlGaAs active region 16,each period including a 10 nm thick GaAs layer and a 10 nm thick Al₀.4Ga₀.6 As layer, a 0.3 μm thick Al₀.4 Ga₀.6 As layer, a 0.3 μm thickAl₀.4 Ga₀.6 As cladding layer 17, and a 50 nm thick GaAs capping layer,25. The light emission takes place from the surface of a facet, 22,which is perpendicular to the plane of the drawing. The modulator isprovided also with electrodes 18 and 19.

The modulator was prepared by depositing upon an about 500 μm thick GaAswafer, to be used as substrate 14 of the modulator semiconductor, layers15-17 and 25 in succession by planar technology deposition. Thedeposition may be carried out by molecular beam epitaxy (MBE), metalorganic vapor phase epitaxy (MOVPE), also known as metal organicchemical vapor deposition (MOCVD), or by hydride vapor phase epitaxy(VPE). In the present embodiment the deposition was carried out by MBE.Thereafter, the coated wafer was patterned with a photoresist mask so asto delineate for trenches parallel to the face intended for lightemission. The width of each trench, about 500 μm, was selected toproduce two lenses, about 250 μm long each, arranged back to back, eachto another. The wafer was then etched using a SiCl₄ plasma to totallyremove in delineated trench areas layers 16, 17, and 25 and a small,about 0.5 μm, thickness of the upper surface of bottom cladding layer15. This small thickness was chosen to allow the etched surface to beabout 0.5 μm beneath the lower boundary of guiding or active region 16.Vertical walls were obtained by etching with plasma using 0.16 W/cm² RFpower and 5 mTorr working pressure. The etched side walls were as smoothas the edge profile of the photoresist mask used for defining thetrenches. The wafer was then thinned down to 150 μm, and 0.5 μm thickSiO₂ layer 20 was deposited at 300° C. by plasma enhanced chemical vapordeposition (PECVD) over the whole of the wafer, namely over top surface21 of capping layer 25, the surface of facet 22 and the etched surface23 of bottom cladding layer 15. The SiO₂ layer serves as the bottomcladding layer for the PEWE lens. Electrodes 18 and 19 may be depositedafter the completion of the structure. Alternatively, the electrodes maybe deposited after the deposition of SiO₂ layer 20. This would requireformation of a window in layer 20 through which electrode 19 is thendeposited.

A 7 μm thick layer of AZ 4620® photoresist was applied by spinning overthe SiO₂ coated surface of the wafer, and thereafter, elongateddiamond-like-shaped photoresist areas 26 (FIG. 4) were patterned in thetrenches centrally between the etched facets and with long apexespointing in the direction of the facets. In FIG. 4, as well as in FIGS.5-8, is shown a little more than one-half of the trench width andassociated photoresists. The dash-and-dot line 27 represents the centerof the trench and of photoresist ("diamond") area 26. Diamond 26 wasfrom 10 to 50 μm wide in the central area and about 250 μm long which isabout one-half the width of the trenches between the devices. Thisallots half of the length of the diamond (about 125 μm) to each ofpackages 10. Other dimensions of the diamond could be used as well solong as the width of the diamond exceeds the width of the area to bematched, e.g., the diameter of the core of the optical fiber. Thediamond was then post-baked at 120° C. for 15 minutes to evaporate mostof the solvent. Thereafter 1 μm thick layer of AZ 4110® photoresist, 28,was spun on the wafer at rotation speeds ranging from 3,000 to 5,000rpm, preferably at 4000 rpm. The two photoresists have similar solventbases; however, the spinning of the AZ 4110® at higher rpms maypartially smear out the diamond patterns. Spinning at lower rpms maylead to a thinner photoresist thickness. Alternatively, 1 μm thickphotoresist could be sprayed on the whole of the surface, including thediamond pattern. In the production of optical packages with otherdevices, the active layer may have thickness and, thus, the height ofthe modal output area of the device, which is more or less than 1 μm. Insuch cases, the rpms should be adjusted to obtain a photoresistthickness matching that of the active layer.

The photoresists used in the specific example are commerciallyobtainable from Electronic Products Division of Hoechst CelaneseCorporation. The AZ 4620® contains 2-Ethoxyethyl Acetate (111-15-9),xylenes (1330-20-7), n-butyl Acetate (123-86-41), Cresol Novolak Resin(9065-82-1) and Diazonaphto guinone sulfonic ester (5610-94-6). The AZ4110® is of the same composition except for the Cresol Novolak Resinwhich is identified as being (117520-84-0). These resists are capable ofbeing remelted and reflowed at temperatures of from 120° to 150° C. andhave refractive indices approximating that of the core of the opticalfiber. This temperature range is below the temperature e.g., 190° C., atwhich the device may be affected unfavorably. Other resists with similarcharacteristics may be also used. For example, the above resists may bereplaced with commercially available resists, such as Shipley 1370® and1195®, both of which contain propylene glycol monoethyl ether acetate(100-65-6).

The wafer was then baked at 120°-150° C. for one hour to allow thediamond shape to remelt and reflow forming a redistributed photoresistshape 28 as shown in FIG. 6. This reflow process resulted in a smoothadiabatic variation of the thickness of the photoresist. The diamondpattern adjacent to the center of each diamond-shaped photoresist area26 retained most of its original thickness (as shown in FIG. 5) of about6-7 μm and a gradual decrease to 1 μm was observed toward the tip of thereflown diamond.

FIGS. 5 or 6 show a step coverage by the 1 μm photoresist over a cornerjoining the top surface of the device and the etched facet. At thisregion, the deposited photoresist expands to almost twice the 1 μmthickness. This type of junction between the polymeric guide and thesemiconductor facet is undesirable. Optical fields conform to theadiabatic guide variations as long as the slope of the guide boundariesis small compared to the divergence of the beam at those points.Expansion of the photoresist layer near the facet to almost twice thedesired thickness means that the optical field emanating from the activeregion will expand to the extent that the photoresist boundaries willallow. From FIG. 5 or 6 it is clear that about 50 percent of the powercould be scattered away from the active area due to the mismatch of theaperture of the photoresist and semiconductor guide active region 16 attheir intersection (i.e. the semiconductor guide is 1 μm thick whereasthe photoresist at that point is about 2 μm thick.) To overcome thisproblem, an angle exposure technique was used. Output light of an argonion laser was filtered to provide 3 mW/cm² of optical flux at 450 nm.The sample was placed at a 5 degree angle tangent to the beam for 12minutes. Because of the dependence of the Fresnel reflection and opticalflux on the incident angle, the photoresist near the etched facets wasprimarily exposed as shown in FIG. 7. Since the optical field conformsto the photoresist boundaries, it is essential to calibrate the exposureand development times to retain≈1 μm thickness of photoresist facingactive region 16 at the etched facet. After development, the photoresistprofile shown in FIG. 8 was obtained.

The device and the lens were then trimmed laterally by Reactive IonEtching (RIE) to their final configurations, and the wafer was baked at120°-150° C. to further smooth out the photoresist boundaries. The waferwas cleaved at the center of the diamond patterns along the center line27 and at some point in the device (modulator) structure resulting inintegrated optical package 10 configuration shown in FIG. 1.

In the preferred embodiment, polymeric photoresist was used for the lensas described above. The resist had refractive index n=1.67 whichapproximated that of the fiber (n_(f) =1.49-1.52). The photoresist wasused because of the ease of handling, treatment and fabrication. Insteadof resists, other organic polymer materials may be used in preparing thewaveguide lens. One of the materials suitable for this purpose ispolyimide with refractive index n=1.6. The use of polyimide requires asomewhat different processing, as is described with reference to FIGS. 9and 10.

Beginning with a wafer processed up to and including dielectric layer 20(FIG. 3), a 6-7 μm thick layer of polyimide, 29, is deposited on top ofdielectric layer 20 (FIG. 9). Thereafter, photoresist deposition,patterning and treatment, as disclosed above with reference to FIGS.4-6, are conducted on top of polyimide layer 29, resulting in thephotoresist profile, 30, (FIG. 9). This photoresist profile is similarto that shown in FIG. 6, except for the thickened coverage of thejuncture between facet 22 and to surface 21 of device 11. Subsequently,the photoresist and underlying polyimide are subjected to dry etching inO₂ plasma (3 sccm O₂ flow, 100 W RF power, 430 V DC bias, with etchingrate of about 70 nm/min). The etching rates of photoresist and polyimideare substantially identical; therefore, photoresist profile 30 istransferred to the polyimide, leading to a lens profile, 31, shown inFIG. 10.

Eighty percent coupling efficiency between an optical fiber tosemiconductor waveguide with an asymmetric modal output area wasachieved using a PEWE lens produced using organic polymeric materials,such as photoresists. In the exemplary embodiment, the semiconductorguide was a modulator structure. Similar coupling efficiencies should beachievable with laser diodes, photodetectors, semiconductor opticalswitches or other structures having asymmetric modal output (or input)areas. For better thermal stability, the PEWE lens process mayincorporate polyimide films.

The measurement of the enhancement of fiber coupling due to the PEWElens was determined using slab waveguide geometry and incident power ofa Nd:YAG laser. From the observation of the near field pattern on theoutput modulator facet, all of the light was coupled into thefundamental mode of the semiconductor guide. An indirect measure of theimprovement in coupling efficiency was observed from the second harmonicsignal radiating from the end facet of the modulator guide. With thesame Nd:YAG incident power, radiated green light from the modulator endfacet was much brighter for the devices containing PEWE lenses comparedto the guides without these lenses. In addition to the large couplingefficiencies, it was possible to easily couple light into the guide andmaintain it for long periods of time. This is due to the large PEWEinput aperture which has roughly the same dimensions as the core of asingle mode fiber.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrated examples shown and described. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

We claim:
 1. An integrated optical package for coupling an opticaldevice having an asymmetric modal area and an optical fiber having acircular modal area, each to another, said package comprising:an opticaldevice with an asymmetric modal area and an elongated wedge-like opticalwaveguide, said optical device and said optical waveguide having acommon substrate, an end portion of said optical waveguide abutting alight emitting (or light receiving) facet of said device, and anopposite end portion of the optical waveguide being for optical couplingto an optical fiber, cross-section of that end of the optical waveguidewhich abuts said facet matching essentially the cross-section of themodal area of the device, and cross-section of the opposite end of theoptical waveguide is designed to match essentially the cross-section ofthe core of the optical fiber, said optical waveguide comprises a planardielectric layer and a wedge-shaped lens of organic polymeric materialon top of the dielectric layer, an upper surface of the dielectric layerand a lower surface of the lens are in alignment with a lower boundaryof an active layer of the device.
 2. The integrated optical package ofclaim 1, in whichsaid lens has a flat bottom, a sloping upper surface,and a cross-section which changes progressively over the length of thelens from that matching the cross-section of the active region of thedevice to that matching the cross-section of the core of the opticalfiber.
 3. The integrated optical package of claim 2, in which saidcross-section changes over a length of 250 μm from one 6-7 μm high to 1μm high.
 4. The integrated optical package claim 1, in which an upperplane of the waveguide is in a form of a truncated triangle with thenarrow, truncated top being adjacent to said facet of the device, andthe broader base being for abutting with an optical fiber.
 5. Theintegrated optical package of claim 1, in which said dielectric layer isSiO₂.
 6. The integrated optical package of claim 1 in which said organicpolymeric material is a polymeric photoresist having an index ofrefraction approximating that of the optical fiber.
 7. The integratedoptical package of claim 1 in which said organic polymeric material is apolyimide.
 8. The integrated optical package of claim 5 in which saidfacet of the device is provided with an anti-reflective coating.
 9. Anoptical lens for coupling an optical component having an asymmetricmodal area and another optical component with a larger modal area, whichcomprises:an elongated wedge-like optical waveguide having end faces atopposite ends of the waveguide, one end face, to be coupled to saidoptical component with the asymmetric modal area, having a cross-sectionmatching said asymmetric modal area, and another end face at an oppositeend of the waveguide, to be coupled to said other optical component,having a cross-section matching said larger modal area, thecross-section of the waveguide progressively changing from said one endface to said another end face, in which said optical waveguide comprisesa planar dielectric layer and a truncated wedge shaped lens of anorganic polymeric material on top of the dielectric layer.
 10. Anoptical lens of claim 9, in which an upper plane of the wedge-likewaveguide is in a form of a truncated triangle with the narrow,truncated top being adjacent to the optical component with saidasymmetric modal area, and the broader base being for abutting to theoptical component with a larger modal area.
 11. An optical lens of claim9, in which said dielectric layer is SiO₂.
 12. An optical lens of claim9, in which said another optical component is an optical fiber, and saidorganic polymeric material is a polymeric photoresist having an index ofrefraction approximately that of the optical fiber.
 13. An optical lensof claim 10, in which said organic polymeric material comprises apolyimide.